1. Technical Field
The present invention relates to an optical transmission system, a receiving-end device, and an optical transmission method and, particularly, to a technique to transmit and receive optical signals having the same information through each of an operational channel and a redundant channel.
2. Background Art
One example of a redundant configuration of the wavelength division multiplexing (WDM) transmission system is a 1:1 configuration where the redundant configuration is composed of an operating transponder for mainly making the wavelength division multiplexing transmission system operate and a redundant transponder for making redundancy separately as a spare. Another example of a redundant configuration of the wavelength division multiplexing transmission system is a 1+1 configuration where the redundant configuration is composed of an operating path and a redundant path and, upon occurrence of an abnormal event in the operating path, capable of switching from the operating path to the redundant path by an optical switch.
However, in the above configurations, it is necessary to prepare the redundant transponder in addition to the operating transponder or prepare the optical switch for switching from the operating path to the redundant path. There is thus a problem that the cost increases to build the redundant configuration. There is also a problem that complicated processing such as switching from the operating transponder to the redundant transponder and switching from the operating path to the redundant path is required.
The redundant configuration systems related to wavelength division multiplexing transmission are disclosed also in WO2010/044154 and Japanese Unexamined Patent Publication No. 2010-056899. However, in the both systems disclosed in those patent literatures, components such as a redundant transponder, an optical switch or an optical coupler are required, and there is still a problem that the cost increases. Further, there is also a problem that complicated processing for switching is required as described above. Thus, those patent literatures do not disclose a technique to solve the above problems, differently from the below-described exemplary embodiment of the invention that solves the above problems through effective utilization of a local selection function.
As described above, in the wavelength division multiplexing transmission system, there are problems that the system is complex and the cost increases when constructing the redundant configuration.